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Abstract:

Provided is a pigment particle suitable for an ink capable of recording
an image that is excellent in color developability and lightfastness, and
has a yellow hue. The pigment particle is a pigment particle having a
structure represented by the following formula (1), in which a maximum
absorption wavelength of an absorption spectrum in a wavelength region of
200 nm or more and 800 nm or less is present in a range of 340 nm or more
and 360 nm or less.
##STR00001##

Claims:

1. A pigment particle having a structure represented by the following
formula (1), wherein a maximum absorption wavelength of an absorption
spectrum in a wavelength region of 200 nm or more and 800 nm or less is
present in a range of 340 nm or more and 360 nm or less. ##STR00004##

2. A pigment particle according to claim 1, wherein the pigment particle
is obtained by: supplying a liquid having dissolved therein a pigment
serving as a raw material to a flow path, which is formed by placing two
surfaces for treatment that rotate relatively to each other at an
interval of 1 mm or less so that the surfaces are opposite to each other;
and precipitating the pigment particle as a fine particle in the flow
path.

3. An ink comprising the pigment particle according to claim 1.

4. An ink according to claim 3, further comprising a 1,2-alkanediol.

5. An ink according to claim 4, wherein a content (% by mass) of the
1,2-alkanediol in the ink is 0.2% by mass or more and 10.0% by mass or
less based on a total mass of the ink.

6. An ink according to claim 3, further comprising a polyoxyethylene
alkyl ether as a surfactant.

7. An ink according to claim 6, wherein a content (% by mass) of the
polyoxyethylene alkyl ether in the ink is 0.05% by mass or more and 2.0%
by mass or less based on a total mass of the ink.

8. An ink according to claim 3, wherein the ink is used for ink jet
recording.

9. An ink cartridge comprising an ink and an ink storage portion for
storing the ink, wherein the ink comprises the ink according to claim 3.

10. An ink jet recording method comprising ejecting an ink from an ink
jet recording head to record an image on a recording medium, wherein the
ink comprises the ink according to claim 3.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a pigment particle having a yellow
hue, and an ink, an ink cartridge, and an ink jet recording method each
using the pigment particle.

[0003] 2. Description of the Related Art

[0004] In recent years, there has been a growing demand for an improvement
in lightfastness of an image recorded by an ink jet recording method. To
cope with such demand, an investigation has been vigorously conducted on
an ink using a pigment as a coloring material. However, an image recorded
with the ink using the pigment as a coloring material has lower color
developability than that of an image recorded with an ink using a dye as
a coloring material. Particularly in the case of an image recorded with a
yellow ink, it has been a subject to achieve both its lightfastness and
color developability.

[0005] In addition, an ideal color tone of a yellow coloring material is
such that its hue angle in a CIE L*a*b* colorimetric system is
90°. In actuality, however, a deviation of the color tone toward
greenish yellow (whose hue angle is larger than 90°), reddish
yellow (whose hue angle is smaller than 90°), or the like occurs
owing to, for example, a light absorption characteristic of a pigment. In
the case of a yellow coloring material to be used in ink jet recording,
the greenish yellow is apt to be recognized as a dull color by the human
eye and hence provides such an impression that image vividness is low.
Accordingly, the reddish yellow is more suitable than the greenish yellow
from the viewpoint of color developability.

[0006] Further, in the ink jet recording, plain paper or a recording
medium having a coating layer (e.g., glossy paper or art paper) has also
become used as a recording medium. Accordingly, it has been such a
demanded that an ink to be used in the ink jet recording be capable of
realizing high color developability in any one of those various recording
media. A method involving using one or more kinds of pigments among C.I.
Pigment Yellows 213, 185, and 155 as coloring materials has been proposed
for achieving both lightfastness and color developability (see Japanese
Patent Application Laid-Open No. 2008-266568).

[0007] In addition, there has been a proposal concerning a method
involving performing a treatment with a microreactor to produce fine
particles of a pigment (International Application No. WO2009/008338).
International Application No. WO2009/008338 discloses that such treatment
with the microreactor can change the crystal form of the pigment, and
describes that α- and γ-type quinacridone pigments were
produced. Meanwhile, International Application No. WO2010/035861 disclose
that when a copper phthalocyanine pigment is subjected to the similar
treatment as disclosed in International Application No. WO2009/008338,
its absorption characteristics in a visible light region become different
from conventional ones, though its crystal form does not change.

SUMMARY OF THE INVENTION

[0008] However, an investigation conducted by the inventors of the present
invention has found that when the ink described in Japanese Patent
Application Laid-Open No. 2008-266568 is used, the lightfastness of an
image to be recorded is secured but its color developability is
insufficient. In addition, C.I. Pigment Yellow 183, 191, or the like has
been known as a pigment having a reddish yellow hue. However, an
investigation conducted by the inventors of the present invention has
found that an image recorded with an ink containing such pigment has low
chroma and cannot obtain color developability. In addition, International
Application No. WO2009/008338 and International Application No.
WO2010/035861 each disclose that treating a pigment by a particular
method can change its crystal form and absorption characteristics.
However, an investigation has been conducted mainly on a quinacridone
pigment or a copper phthalocyanine pigment, and what kind of pigment can
show changes in its crystal form and absorption characteristics, and the
directions of the changes in the absorption characteristics are unclear.

[0009] Therefore, an object of the present invention is to provide a
pigment particle suitable for an ink capable of recording an image that
is excellent in color developability and lightfastness, and has a yellow
hue, and an ink suitable for ink jet recording, an ink cartridge, and an
ink jet recording method each using the pigment particle.

[0010] The object is achieved by the present invention described below.
That is, according to the present invention, provided is a pigment
particle, having a structure represented by the following formula (1), in
which a maximum absorption wavelength of an absorption spectrum in a
wavelength region of 200 nm or more and 800 nm or less is present in a
range of 340 nm or more and 360 nm or less.

##STR00002##

[0011] According to the present invention, provided is a pigment particle
suitable for an ink capable of recording an image that is excellent in
color developability and lightfastness, and has a yellow hue, and an ink
suitable for ink jet recording, an ink cartridge, and an ink jet
recording method each using the pigment particle.

DESCRIPTION OF THE EMBODIMENTS

[0012] Hereinafter, the present invention is described in detail by way of
a preferred embodiment. It should be noted that the abbreviation "C.I."
as used in the description of the specification means "color index." In
addition, the term "maximum absorption wavelength (λmax)"
refers to the wavelength of a peak present at the longest wavelength
among the peaks of an absorption spectrum in 200 nm or more and 800 nm or
less (visible region).

[0013] An investigation conducted by the inventors of the present
invention has found that the effect is obtained by a pigment particle
that has a structure represented by the following formula (1) and whose
λmax is present in the range of 340
nm≦λmax≦360 nm.

##STR00003##

[0014] A compound (pigment) having the structure represented by the
formula (1) has been known as C.I. Pigment Yellow 213. The
λmax of the pigment particles of conventional, general C.I.
Pigment Yellow 213 is present in the range of 370 to 390 nm. In addition,
it has been known that C.I. Pigment Yellow 213 is somewhat inferior in
color developability to other yellow pigments, though its lightfastness
is higher than that of other pigments. In addition, the color tone of
C.I. Pigment Yellow 213 is somewhat greenish yellow.

[0015] An investigation conducted by the inventors of the present
invention has found that the following effect is obtained by causing the
λmax in the visible region of the pigment particles to be
present in the range of 340 to 360 nm which is shorter-wavelength region
in comparison with that of the conventional C.I. Pigment Yellow 213,
while maintaining the molecular structure of C.I. Pigment Yellow 213.
That is, a pigment particle having a color tone whose deviation toward
green is suppressed, and capable of recording such an image that color
developability is improved while lightfastness is maintained is obtained.
When the λmax is present at a wavelength longer than 360 nm,
the color tone is deviated toward a green region. When the
λmax is present at a wavelength shorter than 340 nm, the color
tone is deviated toward an orange region. In other words, once the
λmax deviates from the range, an image to be recorded no
longer has a preferred yellow tone in any case. A possible reason why the
color tone is turned into reddish yellow by causing the λmax
in the visible region to be present in the range of 340 to 360 nm is that
the shift of the λmax to shorter wavelengths can suppress the
absorption of light in a long-wavelength region (yellow to red region).

[0016] Pigment Particle

[0017] The pigment particle of the present invention can be obtained by
common methods of preparing pigment particles that have been
conventionally employed. The methods of preparing pigment particles can
be roughly classified into two methods, i.e., a breakdown method and a
build-up method. The breakdown method is a method involving mechanically
grinding a mixture of a bulk raw material or a raw material compound, a
dispersant, and a solvent with a dispersing apparatus such as a bead mill
to obtain pigment particles. In addition, the build-up method is a method
of obtaining pigment particles from a raw material compound dissolved in
a solvent through a step such as a chemical reaction or precipitation
process, etc. In order that the pigment particle of the present invention
can be obtained, the compound (pigment) having the structure represented
by the formula (1) is used as the raw material.

[0018] A media-type disperser, an ultrasonic disperser, and a
high-pressure collision type disperser can be given as examples of the
dispersing apparatus to be used for general purposes in the breakdown
method. It is also preferred to perform a pre-treatment for the mixture
with a rotation shearing-type stirrer or the like in advance to prevent
clogging in a nozzle or path of the dispersing apparatus before the use
of the dispersing apparatus.

[0019] The media-type disperser can be, for example, such that its
stirring shaft is provided with a disk, a pin, or a ring, or such that
its rotor rotates. It should be noted that the disk to be provided for
the stirring shaft may be a perforated disk, or may be a disk having
formed therein a notch or a groove. Conventionally known apparatus such
as a sand mill, a dyno-mill, and a bead mill can be given as specific
examples of such media-type disperser.

[0020] As the ultrasonic disperser, there can be used a conventionally
known one such as "US-300T" or "US-1200TCVP" (both of which are
manufactured by NIPPON SEIKI CO., LTD.) or "Digital Sonifier 250D"
(manufactured by BRANSON Co.), all of which are trade names.

[0021] For example, a disperser provided with a chamber for pressurizing
the mixture with a high-pressure plunger pump to discharge the mixture
from a small-diameter nozzle can be used as the high-pressure collision
type disperser. A media-less disperser such as a homogenizer or the like
is suitable as the high-pressure collision type disperser. The
pressurizing pressure upon use of the high-pressure collision type
disperser is preferably set to 100 MPa or more. In addition, the number
of times of a treatment with the high-pressure collision type disperser
is preferably set to twice or more.

[0022] The rotation shearing-type stirrer to be used in the pre-treatment
is only required to be a stirrer capable of applying a shear force to the
raw material in the mixture, and a conventionally known batch-type
stirrer or the like can be used. The term "shear force" as used herein
includes a mechanical energy capable of dispersing powder or fine
particles such as an impact force or cavitation as well as a shear
stress. The shear force to be applied to the raw material is preferably
as high as possible. Specifically, the shear rate is set to preferably
104/sec or more, more preferably 105/sec or more. Such high
shear force can be applied by using the following stirrer. The stirrer is
provided with a rotor blade and a fixed portion, the gap between the
rotor blade and the fixed portion is set to be small, and the stirrer can
rotate at a high speed. Specific examples of such stirrer can include
"ULTRA-TURRAX" (manufactured by IKA), "T.K. Homomixer" and "T.K. Filmix"
(both of which are manufactured by PRIMIX Corporation), and "CLEARMIX"
(manufactured by M Technique Co., Ltd.), all of which are trade names.

[0023] On the other hand, a dispersing apparatus generally used in the
build-up method can be, for example, a microchannel-type liquid
processing apparatus (microreactor) used in microchemical process or the
like. Specific examples of the microreactor can include "Micromixer" and
"Microreactor" (both of which are manufactured by IMM), "Microreactor"
(manufactured by CPC Technologies), and "ULREA SS-11" (manufactured by M
Technique Co., Ltd.), all of which are trade names.

[0024] When the pigment particle of the present invention whose
λmax is present in the range of 340 nm or more and 360 nm or
less is prepared, it may be preferred to cause a certain change in the
crystal structure of the pigment serving as a raw material. Here, the
crystal structure of the pigment can be changed by the breakdown method.
However, when pigment particles are prepared by the breakdown method, the
surface of each pigment particle produced by the grinding is apt to have
activity. As a result, pigment particles are apt to aggregate with the
active surface as a core and hence a coarse particle is apt to be formed.
Accordingly, a change over time such as the thickening of a liquid
(pigment dispersion or ink) containing the pigment particles is apt to
occur and hence the dispersion stability of the particles becomes
somewhat insufficient in some cases. Accordingly, it is more preferred to
employ the build-up method rather than the breakdown method upon
preparation of the pigment particle of the present invention.

[0025] When the pigment particle of the present invention whose
λmax is present in the range of 340 nm or more and 360 nm or
less is prepared by the build-up method, the following procedure is
preferred. First, a wet cake containing pigment particles is prepared by
precipitating fine particles from a liquid having dissolved therein a raw
material (pigment coarse material) with the microreactor or the like.
After that, a post-treatment (the dispersion of the pigment particles) is
performed in the presence of a resin dispersant or the like. An apparatus
to be generally utilized upon preparation of an ink for ink jet
recording, such as the media-type disperser, the ultrasonic disperser,
the high-pressure collision type disperser, or the rotation shearing-type
stirrer, can be used in the post-treatment. During the post-treatment,
however, the λmax of the pigment particles is preferably
prevented from changing owing to the dispersion treatment. Accordingly,
conditions during the dispersion such as dispersion time, peripheral
speed, and the kind and particle diameter of a medium to be used as
required are made milder than dispersion conditions during the
preparation of the pigment particle of the present invention by the
breakdown method described in the foregoing. It is also preferred to
adopt the following procedure. After a pigment dispersion containing the
pigment particles at a low concentration has been obtained by treating a
mixture containing the raw material (pigment coarse material) and a
dispersant with the microreactor, the resultant pigment dispersion is
concentrated by a treatment such as ultrafiltration and impurities are
removed from the dispersion.

[0026] By the way, the inventors of the present invention have confirmed
that the lightfastness of an image recorded with a pigment particle whose
λmax is present in 340 nm or more and 360 nm or less reduces
to some degree compared to the C.I. Pigment Yellow 213 having general
light absorption characteristics in some cases. A possible cause for some
degree of reduction of the lightfastness is, for example, a change in
crystallinity of the pigment particle. In addition, an investigation
conducted by the inventors of the present invention has found that the
use of a pigment particle obtained by the following method can suppress a
reduction in lightfastness of an image to be recorded. That is, the
pigment particle of the present invention is preferably a particle
obtained by supplying a liquid having dissolved therein a pigment serving
as a raw material to a flow path, which is formed by placing two surfaces
for treatment that rotate relatively to each other at an interval of 1 mm
or less so that the surfaces are opposite to each other; and
precipitating the pigment as a fine particle in the flow path. A product
with a trade name "ULREA SS-11" (manufactured by M Technique Co., Ltd.)
can be given as an example of the microreactor capable of embodying such
method.

[0027] The inventors of the present invention assume the reason why the
lightfastness of an image recorded with the pigment particle obtained by
the method is improved to be as described below. An apparatus such as the
"ULREA SS-11" is the so-called forced thin film-type microreactor, and a
velocity gradient occurs in the liquid flowing in the flow path by virtue
of relative rotation of the two disks (surfaces for treatment) placed so
as to be capable of approaching, and departing from, each other.
Accordingly, pigment particles having an extremely high sphericity as
compared with that obtained by any other method can be produced. The use
of such pigment particles having a high sphericity leads to the fixation
of the pigment particles in an additionally dense state in a recording
medium. As a result, a reduction in lightfastness of the image to be
recorded can probably be effectively suppressed.

[0028] The pigment particle of the present invention has an average
particle diameter of preferably 10 nm or more and 300 nm or less, more
preferably 10 nm or more and 100 nm or less, particularly preferably 10
nm or more and 50 nm or less. It should be noted that the term "average
particle diameter" as used herein means an average particle diameter on
volume basis (d50). When the average particle diameter is less than
10 nm, the interaction between pigment particles strengthens. In
particular, when the pigment particle is used in an ink, a high level of
storage stability cannot be sufficiently obtained in some cases. In
addition, when the average particle diameter is more than 300 nm, the use
of the pigment particle in a pigment dispersion or an ink may be apt to
cause the sedimentation of the pigment particle. In each example to be
described later, the average particle diameter of the pigment particle
was measured with a dynamic light scattering-type particle
diameter-measuring apparatus (trade name: "UPA-UT151," manufactured by
NIKKISO CO., LTD.) under the following measurement conditions: "particle
permeability" was set to "permeable" and "particle shape" was set to
"nonspherical." Although a sample obtained by diluting the pigment
particle with pure water by a proper factor can be used in the
measurement of the average particle diameter, a surfactant or resin for
aiding the dispersion of the pigment particle, a water-soluble organic
solvent, or the like may be added to the sample as required. In ordinary
cases, the addition of such component to the sample has substantially no
influence on the average particle diameter to be measured. In each
example to be described later, the average particle diameter of the
pigment particle was measured by using a pigment dispersion in a state
where the pigment particle was dispersed with a resin dispersant as a
sample.

[0029] As described in the foregoing, the maximum absorption wavelength
(λmax) is defined as the wavelength of a peak present at the
longest wavelength among the peaks of an absorption spectrum in 200 nm or
more and 800 nm or less (visible region). When the absorption spectrum is
measured by utilizing an aqueous liquid containing the pigment particle,
a peak derived from a component other than the pigment such as a solvent
or a resin can be present at around 200 nm. Accordingly, in the present
invention, a wavelength that provides a peak present at longer
wavelengths of the visible region is defined as the λmax. In
particular, in the present invention, the λmax of the pigment
particle having the structure represented by the formula (1) as a yellow
coloring material is specified. Therefore, in an additionally strict
sense, the λmax can probably be defined as a wavelength that
provides the largest absorption peak in an absorption spectrum in 300 nm
or more and 500 nm or less (yellow region).

[0030] The maximum absorption wavelength (λmax) of the
absorption spectrum of the pigment particle can be measured according to
a general method. In each example to be described later, the
λmax of the absorption spectrum of a liquid containing the
pigment particle of the present invention was measured with a
spectrophotometer (trade name: "U-3310," manufactured by Hitachi
High-Technologies Corporation). It should be noted that during the
measurement, the sampling interval was set to 0.5 nm, and peak detection
was performed under the conditions of a threshold of 0.01 and a
sensitivity of 1. A liquid obtained by diluting the pigment particle with
pure water by such a proper factor that its absorbance at the
λmax is about 1.0 is preferably used as a sample in the
measurement. A surfactant or resin for aiding the dispersion of the
pigment particle, a water-soluble organic solvent, or the like may be
added to the sample as required. In ordinary cases, the addition of such
component to the sample has substantially no influence on the
λmax to be measured. In each example to be described later,
the λmax of the pigment particle was measured by using a
pigment dispersion in a state where the pigment particle was dispersed
with a resin dispersant as a sample. On the other hand, a component such
as a coloring material having an absorption wavelength in the visible
region needs to be prevented from being incorporated into the measurement
sample because the component may affect the λmax to be
measured for the pigment particle having the structure represented by the
formula (1). In other words, when the inclusion of an unnecessary
component (e.g., another coloring material) in the sample as a measuring
object is expected, the sample from which such component has been removed
is prepared and subjected to the measurement.

[0031] Ink

[0032] An ink of the present invention contains the pigment particle of
the present invention. Hereinafter, a component constituting the ink of
the present invention and the like are described in detail.

[0033] Pigment Particle

[0034] The pigment particle of the present invention is incorporated into
the ink of the present invention. The content (% by mass) of the pigment
particle in the ink is preferably 0.1% by mass or more and 10.0% by mass
or less, more preferably 0.1% by mass or more and 5.0% by mass or less
based on the total mass of the ink. It should be noted that a pigment
different from the pigment particle of the present invention or a dye may
be used in combination as a coloring material for the ink in addition to
the pigment particle.

[0035] The manner in which the pigment particle is dispersed in the ink of
the present invention is not limited. A resin-dispersed pigment using a
resin as a dispersant, a pigment dispersed with a surfactant, and a
microcapsule pigment obtained by covering at least part of the surface of
the pigment particle with a resin or the like can be given as an example.
Of those, a resin-dispersed pigment obtained by causing a resin as a
dispersant to physically adsorb to the surface of a pigment particle and
dispersing the pigment particle by means of the action of the resin is
preferred. The resin dispersant is preferably capable of dispersing the
pigment particle in an aqueous medium by means of the action of an
anionic group or a nonionic group. A conventionally known copolymer that
can be used in an ink for ink jet recording or a salt thereof can be used
as the resin dispersant. A more suitable resin dispersant is, for
example, a copolymer having such a hydrophilic unit and a hydrophobic
unit as listed below. The hydrophilic unit is, for example, a unit
derived from a hydrophilic monomer such as a monomer having a carboxy
group such as (meth)acrylic acid or a salt thereof. In addition, the
hydrophobic unit is, for example, a unit derived from a hydrophobic
monomer such as styrene or a derivative thereof, a monomer having an
aromatic ring such as benzyl (meth)acrylate, or a monomer having an
aliphatic group such as a (meth)acrylate.

[0036] 1,2-Alkanediol

[0037] An investigation conducted by the inventors of the present
invention has found the following new problem. When the ink containing
the pigment particle of the present invention is used, the color
developability (chroma) of an image recorded by using the art paper as a
recording medium reduces to some degree in some cases. The art paper,
which is a recording medium having a coating layer, has a coating layer
whose pore size is larger than that of the so-called glossy paper.
Accordingly, the following tendency arises. The pigment particle is apt
to sink into the paper and hence the color developability of the paper is
apt to be lower than that of the glossy paper. An investigation conducted
by the inventors of the present invention with a view to solving such
problem has found that the addition of a 1,2-alkanediol to the ink
improves the color developability of even the image recorded in the art
paper.

[0038] In ordinary cases, the use of the ink containing the 1,2-alkanediol
leads to a reduction in color developability of an image recorded by
using the art paper as a recording medium because the permeability of the
ink into the recording medium is raised and hence the pigment particle is
apt to sink into the recording medium. In contrast, in the ink of the
present invention, the addition of the 1,2-alkanediol can suppress a
reduction in color developability of an image recorded by using the art
paper as a recording medium. The inventors of the present invention
assume the mechanism via which the reduction in color developability of
the image can be suppressed by the addition of the 1,2-alkanediol as
described above to be as described below.

[0039] A dispersion treatment causes a certain physical or chemical change
in the surface of the pigment particle. The color developability of the
image probably reduces because the pigment particle whose surface has
undergone the certain change is apt to sink into the recording medium.
The 1,2-alkanediol is a compound having a hydrophilic portion and a
hydrophobic portion in its structure. That is, the 1,2-alkanediol is a
compound having a structure like a surfactant but its molecular weight is
extremely small as compared with that of a general surfactant.
Accordingly, when pigment particles dispersed with a resin dispersant are
used, the resin adsorbs to the surface of pigment particles but the
1,2-alkanediol enters a slight gap in the surface to be present in a
state of keeping an appropriate adsorption-desorption equilibrium with
respect to the surface of the pigment particle. In addition, the action
of the 1,2-alkanediol facilitates the aggregation of the pigment
particles and hence the sinking of the pigment particles into the
recording medium is probably suppressed.

[0040] In view of the foregoing, the 1,2-alkanediol is preferably
incorporated into the ink of the present invention. The 1,2-alkanediol is
preferably such a 1,2-alkanediol as to be a liquid at normal temperature
(25° C.) such as 1,2-propanediol, 1,2-butanediol, or
1,2-pentanediol because such 1,2-alkanediol easily dissolves in the
aqueous medium constituting the ink and hence the above-mentioned action
easily occurs.

[0041] When the 1,2-alkanediol is used, the content (% by mass) of the
1,2-alkanediol in the ink is preferably 0.2% by mass or more and 10.0% by
mass or less, more preferably 1.0% by mass or more and 5.0% by mass or
less based on the total mass of the ink. When the content of the
1,2-alkanediol is less than 0.2% by mass, the following tendency arises.
A suppressing action on the sinking of the pigment particles into the
recording medium hardly occurs and hence an improving effect on the color
developability is hardly obtained. On the other hand, when the content of
the 1,2-alkanediol is more than 10.0% by mass, the ejectability of the
ink tends to be apt to reduce owing to the facilitation of the
aggregation of the pigment particles even in the ink, with the result
that sufficient color developability is not obtained in some cases.

[0042] Polyoxyethylene Alkyl Ether

[0043] A polyoxyethylene alkyl ether is preferably incorporated as a
surfactant into the ink of the present invention. The incorporation of
the polyoxyethylene alkyl ether can additionally improve the color
developability of an image recorded by using, in particular, glossy paper
as a recording medium. The polyoxyethylene alkyl ether has a retarding
action on the permeation and drying of an ink droplet in the recording
medium. Accordingly, the compatibility between an ink dot applied earlier
to the recording medium and an ink dot applied later thereto is improved.
As a result, a pigment layer to be formed on the recording medium becomes
additionally smooth, and hence the glossiness of the image can be
improved and its color developability can also be improved. When
multi-path recording (a method involving recording an image in a unit
region such as one band or one pixel through multiple times of scanning
with a recording head) effective in recording a high-definition image is
performed, it is particularly effective to use the ink containing the
polyoxyethylene alkyl ether. This is because of the following reason.
When the multi-path recording is performed, an image hardly becomes
smooth because the time interval during which multiple dots are formed
enlarges. However, the use of the polyoxyethylene alkyl ether can
smoothen the image even when the multi-path recording is performed.

[0044] The polyoxyethylene alkyl ether is a compound having a high
molecular weight. Accordingly, the rate at which the polyoxyethylene
alkyl ether evaporates from a recording medium and the rate at which the
polyoxyethylene alkyl ether permeates the recording medium are moderate.
In addition, the polyoxyethylene alkyl ether easily becomes compatible
with each of a hydrophilic substance and a lipophilic substance because
the polyoxyethylene alkyl ether is a compound having a polyoxyethylene
chain and a hydrocarbon chain in its structure. As a result, ink dots
overlap each other in a liquid state and easily fit to the recording
medium. Accordingly, the dot height can be suppressed to a low level, and
the glossiness and color developability of an image can be improved.
Further, the polyoxyethylene alkyl ether does not inhibit a reaction
between a cationic substance in the recording medium and an anionic
component (such as the resin dispersant) in the ink, and can efficiently
bond both the substance and the component because the polyoxyethylene
alkyl ether is a nonionic compound. Accordingly, the pigment particle can
be fixed to the surface of the recording medium or the vicinity thereof.

[0045] The polyoxyethylene alkyl ether has a structure represented by a
general formula "R--O--(CH2CH2O)mH." In the general
formula, R represents a hydrocarbon group and m represents an integer.
The number of carbon atoms of R (alkyl group) in the general formula as
the hydrophobic group of the polyoxyethylene alkyl ether to be
incorporated into the ink of the present invention is preferably 12 to
22. More specifically, R in the general formula preferably represents a
lauryl group (12), a cetyl group (16), a stearyl group (18), an oleyl
group (18), a behenyl group (22), or the like (a numerical value in
parentheses represents the number of carbon atoms of the hydrocarbon
group). In addition, m in the general formula representing the number of
ethylene oxide groups as the hydrophilic groups of the polyoxyethylene
alkyl ether represents preferably 10 or more and 50 or less, more
preferably 10 or more and 40 or less.

[0046] The content (% by mass) of the polyoxyethylene alkyl ether in the
ink is preferably 0.05% by mass or more and 2.0% by mass or less, more
preferably 0.2% by mass or more and 1.0% by mass or less based on the
total mass of the ink. When the content of the polyoxyethylene alkyl
ether is less than 0.05% by mass, an improving effect on compatibility
between multiple dots on the surface of a recording medium tends to be
insufficient. Accordingly, the smoothness of a pigment layer to be formed
on the surface of the recording medium reduces to some degree and hence
the glossiness of an image reduces, which may resultantly lead to a
reduction in color developability of an image recorded by using glossy
paper as the recording medium. On the other hand, when the content of the
polyoxyethylene alkyl ether is more than 2.0% by mass, the following
tendency arises. Competitive adsorption of the polyoxyethylene alkyl
ether and the resin dispersant to the surface of the pigment particle
becomes remarkable, and hence the nonionicity of the surface of the
pigment particle strengthens. As a result, a bond between the resin
dispersant having an anionic group for dispersing the pigment particle
and a cationic substance in the recording medium weakens, and hence the
pigment particle is apt to sink into the recording medium particularly in
the case where the medium is art paper or plain paper. Accordingly, the
color developability reduces to some degree in some cases.

[0047] The polyoxyethylene alkyl ether has an HLB value determined by
Griffin's method of preferably 13.0 or more, more preferably 15.0 or
more. When the HLB value is less than 13.0, an alleviating action on the
fixation of a dot reduces and hence an improving effect on color
developability is not obtained in some cases. It should be noted that the
upper limit for the HLB value is 20.0 as described later. Accordingly,
the upper limit for the HLB value of the polyoxyethylene alkyl ether to
be suitably used in the present invention is also 20.0 or less.

[0048] Here, Griffin's method that specifies the HLB value of a surfactant
is described. An HLB value based on Griffin's method is determined from
the formula weight of a hydrophilic group of a surfactant and the
molecular weight of the surfactant by using the following equation (2).
The HLB value, which falls within the range of 0.0 to 20.0, represents
the degree of the hydrophilicity or lipophilicity of a surfactant. A
lower HLB value means that the lipophilicity (hydrophobicity) of the
surfactant is higher. On the other hand, a higher HLB value means that
the hydrophilicity of the surfactant is higher.

HLB value=20×(formula weight of hydrophilic group of
surfactant)/(molecular weight of surfactant) (2)

[0049] Aqueous Medium

[0050] An aqueous medium that is water or a mixed solvent of water and a
water-soluble organic solvent can be incorporated into the ink of the
present invention. Deionized water is preferably used as water. The water
content (% by mass) in the ink is preferably 50.0% by mass or more and
95.0% by mass or less based on the total mass of the ink. The ink of the
present invention is preferably an aqueous ink containing at least water
as the aqueous medium. In addition, any one of the solvents that can be
used in inks for ink jet recording such as alcohols, glycol ethers, and
nitrogen-containing compounds can be used as the water-soluble organic
solvent, and one or two or more kinds thereof can be incorporated into
the ink. The content (% by mass) of the water-soluble organic solvent in
the ink is preferably 3.0% by mass or more and 50.0% by mass or less
based on the total mass of the ink. It should be noted that the content
of the water-soluble organic solvent is a value including the
1,2-alkanediol to be used as required.

[0051] Other Components

[0052] A water-soluble organic compound that is a solid at normal
temperature such as urea or a derivative thereof, trimethylolpropane, or
trimethylolethane in addition to the above-described components may be
incorporated into the ink of the present invention. The content (% by
mass) of the water-soluble organic solvent that is a solid at normal
temperature in the ink is preferably 0.1% by mass or more and 20.0% by
mass or less, more preferably 3.0% by mass or more and 10.0% by mass or
less based on the total mass of the ink. In addition, various other
additives such as a surfactant, a pH adjustor, a defoaming agent, a rust
inhibitor, an antiseptic, a mildewproofing agent, an antioxidant, a
reduction inhibitor, an evaporation accelerator, and a chelating agent
may be incorporated as required.

[0053] Ink Cartridge

[0054] An ink cartridge of the present invention is provided with an ink
and an ink storage portion for storing the ink. In addition, the ink
stored in the ink storage portion is the ink of the present invention
described in the foregoing. The structure of the ink cartridge is, for
example, such that the ink storage portion is constituted of an ink
storage chamber for storing a liquid ink and a negative
pressure-generating member storage chamber for storing a negative
pressure-generating member for holding the ink in itself with a negative
pressure. Alternatively, the ink cartridge may be such that the ink
storage portion does not have an ink storage chamber for storing a liquid
ink and is constituted so as to hold the total amount to be stored with
the negative pressure-generating member. Further, the ink cartridge may
be constituted so as to have the ink storage portion and a recording
head.

[0055] Ink Jet Recording Method

[0056] An ink jet recording method of the present invention is a method
including ejecting the ink of the present invention described in the
foregoing from an ink jet recording head to record an image on a
recording medium. A mode of ejecting the ink is, for example, a mode
involving applying a mechanical energy to the ink or a mode involving
applying a thermal energy to the ink. An ink jet recording method
involving utilizing a thermal energy is particularly preferably adopted
in the present invention. The process of the ink jet recording method may
be known ones except that the ink of the present invention is used.
Although any recording medium may be used as the recording medium, paper
having permeability such as plain paper and a recording medium having a
coating layer (e.g., glossy paper or art paper) is preferably used. Of
those, the recording medium having a coating layer capable of causing at
least part of the pigment particles in the ink to be present on the
surface of the recording medium or the vicinity thereof is particularly
preferably used. Such recording medium can be selected according to, for
example, the intended use of a recorded product in which the image has
been recorded. Examples of the recording medium include: glossy paper
suitable for obtaining an image having a photo-quality glossy feeling;
and art paper taking advantage of the texture of a base material (e.g.,
drawing paper texture, canvas texture, or Japanese paper texture) for
representing a picture, a photograph, a graphic image, and the like
according to one's liking.

[0057] The ink of the present invention can be used as an ink set by being
combined with another ink. One or two or more kinds can be selected from,
for example, cyan, magenta, yellow, black, red, green, and blue inks as
the hue of the other ink. Multiple inks identically having the same hue
as that of any such ink as described above and different from each other
in pigment content may also be used as inks constituting the ink set.

EXAMPLES

[0058] Next, the present invention is described more specifically by way
of examples and comparative examples. However, the present invention is
not limited to the following examples unless going beyond the gist
thereof. It should be noted that the terms "part(s)" and "%" each used
for describing the usage of a component refer to "part(s) by mass" and "%
by mass," respectively unless otherwise stated. In addition, a product
with a trade name "HOSTAPERM Yellow H5G" (manufactured by Clariant Co.)
was used as C.I. Pigment Yellow 213. In addition, a product with a trade
name "PALIOTOLE Yellow K2270" (manufactured by BASF Co.) was used as C.I.
Pigment Yellow 183.

[0059] Preparation of Wet Cake Containing Pigment Particles

[0060] Wet Cake 1

[0061] 1,500 milliliters of a solution obtained by dissolving acetic acid
in methanol (1.0% acetic acid solution) was prepared as a liquid A. In
addition, 90 mL of a solution obtained by dissolving 2.0 parts of C.I.
Pigment Yellow 213 in a mixed liquid of 78.4 parts of dimethylsulfoxide
(reagent grade) and 19.6 parts of 0.5-mol/L potassium hydroxide (ethanol
solution) was prepared as a liquid B. A treatment based on the build-up
method was performed with a microreactor (trade name: "ULREA SS-11,"
manufactured by M Technique Co., Ltd.) while the temperature of the
liquid A was set to 5° C., the temperature of the liquid B was set
to 25° C., the flow rate of the liquid A was set to 50 mL/min, and
the flow rate of the liquid B was set to 3 mL/min. After the treatment,
the resultant was filtered with a Buchner funnel. Thus, a paste was
obtained. The resultant paste was washed with ion-exchanged water three
times and then a proper amount of ion-exchanged water was added to the
washed product. Thus, a wet cake 1 having a pigment particle (solid
matter) content of 15.0% was prepared.

[0062] Wet Cake 2

[0063] The same liquid A and liquid B as those used upon preparation of
the "wet cake 1" were prepared. A treatment based on the build-up method
was performed with a microreactor (trade name: "CYTOS Lab System-2000,"
manufactured by CPC Technologies) while the flow rate of the liquid A was
set to 10 mL/min and the flow rate of the liquid B was set to 0.6 mL/min.
After the treatment, the resultant was filtered with a Buchner funnel.
Thus, a paste was obtained. The resultant paste was washed with
ion-exchanged water three times and then a proper amount of ion-exchanged
water was added to the washed product. Thus, a wet cake 2 having a
pigment particle (solid matter) content of 15.0% was prepared.

[0064] Wet Cake 3

[0065] The same liquid A and liquid B as those used upon preparation of
the "wet cake 1" were prepared. A treatment based on the build-up method
was performed with a micromixer (trade name: "HPIMM-Las45250,"
manufactured by IMM Co.) while the flow rate of the liquid A was set to
10 mL/min and the flow rate of the liquid B was set to 0.6 mL/min. After
the treatment, the resultant was filtered with a Buchner funnel. Thus, a
paste was obtained. The resultant paste was washed with ion-exchanged
water three times and then a proper amount of ion-exchanged water was
added to the washed product. Thus, a wet cake 3 having a pigment particle
(solid matter) content of 15.0% was prepared.

[0066] Wet Cake 4

[0067] A liquid B was prepared in the same manner as in the case of the
"wet cake 1" except that C.I. Pigment Yellow 183 was used instead of C.I.
Pigment Yellow 213. Then, a wet cake 4 having a pigment particle (solid
matter) content of 15.0% was prepared in the same manner as in the case
of the "wet cake 1" except that the liquid B thus prepared was used.

[0068] Each pigment used as a raw material and each wet cake obtained in
the foregoing were subjected to NMR analysis. As a result, it was
confirmed that 1H and 13C spectra after the treatment coincided
with those before the treatment. Accordingly, it was confirmed that each
pigment particle in each wet cake thus prepared had the same molecular
structure as that of the pigment used as a raw material. It should be
noted that the NMR analysis was performed by using a solution obtained by
dissolving a wet cake containing a powdery pigment used as a raw material
or pigment particles in a mixture of DMSO-d6 and 0.5-mol/L potassium
hydroxide (ethanol solution) as a sample under the conditions of normal
temperature (25° C.) and 400 MHz.

[0069] Preparation of Pigment Dispersion

[0070] Pigment Dispersion Containing Pigment Particles 1

[0071] 70.0 Parts of the wet cake 1, 24.0 parts of an aqueous solution of
a resin dispersant 1 (having a resin (solid matter) content of 25.0%),
and 6.0 parts of water were mixed. It should be noted that the resin
dispersant 1 is obtained by neutralizing a styrene-acrylic acid copolymer
(trade name: "JONCRYL 680," acid value: 215 mgKOH/g, weight-average
molecular weight: 4,900, manufactured by BASF Co.) with potassium
hydroxide so that the neutralization equivalent is 0.85. Then, the
mixture was subjected to a dispersion treatment with a rotation
shearing-type stirrer (trade name: "CLM-2.2S," manufactured by M
Technique Co., Ltd.) for 60 minutes at 3,500 rpm. After that, the
resultant was centrifuged at a rotational frequency of 5,000 rpm for 30
minutes. Thus, an aggregate component was removed. The remainder was
diluted with ion-exchanged water. Thus, a pigment dispersion containing
pigment particles 1 having an average particle diameter of 18 nm and a
maximum absorption wavelength λmax of 351 nm was obtained. The
content of the pigment particles 1 in the resultant pigment dispersion
was 10.0%.

[0072] Pigment Dispersion Containing Pigment Particles 2

[0073] The same treatments as in the case of the "pigment particles 1"
were carried out except that 70.0 parts of the wet cake 1, 15.0 parts of
a resin dispersant 2 (having a resin (solid matter) content of 40.0%),
and 15.0 parts of water were used. It should be noted that the resin
dispersant 2 is obtained by neutralizing a styrene-butyl acrylate-acrylic
acid copolymer (acid value: 120 mgKOH/g, weight-average molecular weight:
10,000) with potassium hydroxide so that the neutralization equivalent is
0.85. Thus, a pigment dispersion containing pigment particles 2 having an
average particle diameter of 20 nm and a maximum absorption wavelength
λmax of 352 nm was obtained. The content of the pigment
particles 2 in the resultant pigment dispersion was 10.0%.

[0074] Pigment Dispersion Containing Pigment Particles 3

[0075] 60.0 Parts of the wet cake 1, 24.0 parts of an aqueous solution of
the resin dispersant 1 (having a resin (solid matter) content of 25.0%),
and 16.0 parts of water were mixed. The mixture was subjected to a
dispersion treatment with an ultrasonic disperser (trade name: "US-300T,"
manufactured by NIPPON SEIKI CO., LTD.) at an output of 300 W for 60
minutes. After that, the resultant was centrifuged at a rotational
frequency of 5,000 rpm for 30 minutes. Thus, an aggregate component was
removed. The remainder was diluted with ion-exchanged water. Thus, a
pigment dispersion containing pigment particles 3 having an average
particle diameter of 22 nm and a maximum absorption wavelength
λmax of 350 nm was obtained. The content of the pigment
particles 3 in the resultant pigment dispersion was 10.0%.

[0076] Pigment Dispersion Containing Pigment Particles 4

[0077] A pigment dispersion containing pigment particles having an average
particle diameter of 16 nm and a maximum absorption wavelength
λmax of 341 nm was obtained in the same manner as in the case
of the "pigment particles 1" except that the wet cake 2 was used instead
of the wet cake 1. The content of the pigment particles 4 in the
resultant pigment dispersion was 10.0%.

[0078] Pigment Dispersion Containing Pigment Particles 5

[0079] 10.5 Parts of C.I. Pigment Yellow 213, 24.0 parts of an aqueous
solution of the resin dispersant 1 (having a resin (solid matter) content
of 25.0%), and 65.5 parts of water were mixed. The resultant mixture was
loaded into a bead mill (trade name: "LMZ2," manufactured by Ashizawa
Finetech Ltd.) filled with zirconia beads having a diameter of 0.1 mm at
a ratio of 80.0%, and was then subjected to a dispersion treatment at a
peripheral speed of 12 m/s for 5 hours. After that, the resultant was
centrifuged at a rotational frequency of 5,000 rpm for 30 minutes. Thus,
an aggregate component was removed. The remainder was diluted with
ion-exchanged water. Thus, a pigment dispersion containing pigment
particles 5 having an average particle diameter of 48 nm and a maximum
absorption wavelength λmax of 358 nm was obtained. The content
of the pigment particles 5 in the resultant pigment dispersion was 10.0%.

[0080] Pigment Dispersion Containing Pigment Particles 6

[0081] A pigment dispersion containing pigment particles having an average
particle diameter of 18 nm and a maximum absorption wavelength
λmax of 338 nm was obtained in the same manner as in the case
of the "pigment particles 1" except that the wet cake 3 was used instead
of the wet cake 1. The content of the pigment particles 6 in the
resultant pigment dispersion was 10.0%.

[0082] Pigment Dispersion Containing Pigment Particles 7

[0083] 10.5 Parts of C.I. Pigment Yellow 213, 24.0 parts of an aqueous
solution of the resin dispersant 1 (having a resin (solid matter) content
of 25.0%), and 65.5 parts of water were mixed. The resultant mixture was
subjected to three paths of a dispersion treatment with a high-pressure
collision type disperser (trade name: "Nanomizer," manufactured by
YOSHIDA KIKAI CO., LTD.) at a pressure of 150 MPa. After that, the
resultant was centrifuged at a rotational frequency of 5,000 rpm for 30
minutes. Thus, an aggregate component was removed. The remainder was
diluted with ion-exchanged water. Thus, a pigment dispersion containing
pigment particles 7 having an average particle diameter of 55 nm and a
maximum absorption wavelength λmax of 362 nm was obtained. The
content of the pigment particles 7 in the resultant pigment dispersion
was 10.0%.

[0084] Pigment Dispersion Containing Pigment Particles 8

[0085] 10.5 Parts of C.I. Pigment Yellow 213, 24.0 parts of an aqueous
solution of the resin dispersant 1 (having a resin (solid matter) content
of 25.0%), and 65.5 parts of water were mixed. The resultant mixture was
loaded into a glass container filled with zirconia beads having a
diameter of 0.3 mm at a ratio of 50.0%, and was then subjected to a
dispersion treatment for 8 hours with a simple disperser (paint shaker,
trade name: "DAS200-K," manufactured by Lau Industries). After that, the
resultant was centrifuged at a rotational frequency of 5,000 rpm for 30
minutes. Thus, an aggregate component was removed. The remainder was
diluted with ion-exchanged water. Thus, a pigment dispersion containing
pigment particles 8 having an average particle diameter of 125 nm and a
maximum absorption wavelength λmax of 382 nm was obtained. The
content of the pigment particles 8 in the resultant pigment dispersion
was 10.0%.

[0086] Pigment Dispersion Containing Pigment Particles 9

[0087] 10.5 Parts of C.I. Pigment Yellow 213, 34.5 parts of an aqueous
solution of the resin dispersant 3 (having a resin (solid matter) content
of 38.0%), and 55.0 parts of water were mixed. It should be noted that
the resin dispersant 3 is obtained by neutralizing a styrene-acrylic acid
copolymer (acid value: 210 mgKOH/g, weight-average molecular weight:
10,000) with ammonia water so that the neutralization equivalent is 0.85.
Glass beads having a diameter of 1.7 mm were added to the resultant
mixture and then the whole was subjected to a dispersion treatment with a
sand mill (manufactured by YASUKAWA SEISAKUSHO CO., LTD.) for 2 hours.
After that, the resultant was centrifuged at a rotational frequency of
5,000 rpm for 30 minutes. Thus, an aggregate component was removed. The
remainder was diluted with ion-exchanged water. Thus, a pigment
dispersion containing pigment particles 9 having an average particle
diameter of 95 nm and a maximum absorption wavelength λmax of
378 nm was obtained. The content of the pigment particles 9 in the
resultant pigment dispersion was 10.0%.

[0088] Pigment Dispersion Containing Pigment Particles 10

[0089] 60.0 Parts of the wet cake 4, 24.0 parts of an aqueous solution of
the resin dispersant 1 (having a resin (solid matter) content of 25.0%),
and 16.0 parts of water were mixed. The resultant mixture was subjected
to a dispersion treatment with an ultrasonic disperser (trade name:
"US-300T," manufactured by NIPPON SEIKI CO., LTD.) at an output of 300 W
for 1 hour. After that, the resultant was centrifuged at a rotational
frequency of 5,000 rpm for 30 minutes. Thus, an aggregate component was
removed. The remainder was diluted with ion-exchanged water. Thus, a
pigment dispersion containing pigment particles 10 having an average
particle diameter of 22 nm and a maximum absorption wavelength
λmax of 360 nm was obtained. The content of the pigment
particles 10 in the resultant pigment dispersion was 10.0%.

Preparation of Inks

Examples 1 to 20 and Comparative Examples 1 to 5

[0090] Respective components (unit: %) shown in Tables 1-1 to 1-3 were
mixed with each other and thoroughly stirred. After that, pressure
filtration was performed with a membrane filter having a pore size of 1.2
μm (trade name "HDC II Filter," manufactured by Pall Corporation) to
prepare each ink. It should be noted that details of trade names in
Tables 1-1 to 1-3 are shown below.

[0099] An ink cartridge filled with each ink obtained in the foregoing was
set in an ink jet recording apparatus mounted with a recording head for
ejecting an ink by means of thermal energy (trade name: "PIXUS Pro9500
Mark II," manufactured by Canon Inc.). In the ink jet recording
apparatus, an image recorded under such a condition that 8 ink droplets
each having a mass of 3.5 ng are applied to a unit region measuring 1/600
inch× 1/600 inch at a resolution of 600 dpi×600 dpi is
defined as having "a recording duty of 100%." A pattern including two
kinds of solid images having recording duties of 50% and 100% was
recorded on each of glossy paper and art paper. It should be noted that a
product with a trade name "Canon Photo Paper-Gloss Pro (platinum grade)
PT101" (manufactured by Canon Inc.) was used as the glossy paper. In
addition, a product with a trade name "Fine Art Paper Photo Rag"
(manufactured by Canon Inc.) was used as the art paper. The resultant
recorded products were air-dried for 24 hours and then evaluated for the
following respective items. It should be noted that a spectrophotometer
based on a CIE L*a*b* colorimetric system (trade name: "Spectrolino,"
manufactured by Gretag Macbeth Co.) was used in the colorimetry of an
image. In the present invention, evaluation criteria "C," "B," and "A" in
each of the following evaluation items corresponded to an unacceptable
level, an acceptable level, and an excellent level, respectively. Table 2
shows the results of the evaluations.

[0100] Color Developability in Glossy Paper

[0101] The solid image having a recording duty of 100% in the recorded
product obtained by using the glossy paper was evaluated for its color
developability in the glossy paper by measuring values for its hue angle
(h) and chroma (c*) under the condition of a light source of D50.
Evaluation criteria are as described below.

A: The hue angle was 75° or more and 90° or less, and the
chroma was 95 or more. B: The hue angle was 75° or more and
90° or less, and the chroma was less than 95. C: The hue angle was
less than 75° or more than 90°.

[0102] Color Developability in Art Paper

[0103] The solid image having a recording duty of 100% in the recorded
product obtained by using the art paper was evaluated for its color
developability in the art paper by measuring a value for its chroma (c*)
under the condition of a light source of D50. Evaluation criteria are as
described below.

A: The chroma was 85 or more. B: The chroma was 82 or more and less than
85. C: The chroma was less than 82.

[0104] Lightfastness

[0105] The recorded product obtained by using the glossy paper was loaded
into a xenon weatherometer (trade name: "Ci4000," manufactured by Atlas
Co.) and then irradiated with xenon light for 200 hours under the
conditions of a radiation intensity of 0.39 W/m2, a black panel
temperature of 63° C., and a relative humidity of 70%. Values for
the optical densities of the solid image having a recording duty of 50%
in the recorded product before and after the irradiation were measured,
and then the image was evaluated for its lightfastness based on a value
calculated from an equation "residual ratio of optical density
(%)=(optical density after irradiation/optical density before
irradiation)×100." Evaluation criteria are as described below.

A: The residual ratio of optical density was 80% or more. B: The residual
ratio of optical density was 70% or more and less than 80%. C: The
residual ratio of optical density was less than 70%.

TABLE-US-00004
TABLE 2
Results of evaluations
Color developability Color developability Light-
in glossy paper in art paper fastness
Example 1 A A A
2 A A A
3 A A A
4 A A B
5 A A B
6 A A A
7 A A A
8 A B A
9 A B A
10 A A A
11 A A A
12 B B A
13 A A A
14 A A A
15 B A A
16 B A A
17 A A A
18 A A A
19 A B A
20 B B B
Comparative 1 C A B
Example 2 C A A
3 C A A
4 C A A
5 B C C

[0106] It should be noted that the color developability in the art paper
of Example 8 was somewhat inferior to the color developability in the art
paper of Example 9. In addition, the color developability in the glossy
paper of Example 15 was somewhat inferior to the color developability in
the glossy paper of Example 16.

[0107] While the present invention has been described with reference to
exemplary embodiments, it is to be understood that the invention is not
limited to the disclosed exemplary embodiments. The scope of the
following claims is to be accorded the broadest interpretation so as to
encompass all such modifications and equivalent structures and functions.

[0108] This application claims the benefit of Japanese Patent Application
No. 2011-195799, filed Sep. 8, 2011, which is hereby incorporated by
reference herein in its entirety.